Process for recovery of hydrocarbons by in situ combustion



Oct. 17, 1961 H. w. PARKER ETAL 3,004,596

PROCESS FOR RECOVERY OF HYDROCARBONS BY IN SITU COMBUSTION Filed March 28, 1958 22 AIR SUPPLY PRODUCT I PRODUCTION 29 24 I WELL AUXILIARY WELL SELECTIVE FRACTUR I NG I I I- III ml FIG. 2

ATTORNEYS Tnited States This invention relates to a process for producing hydrocarbons from a carbonaceous stratum by in situ'combus tion.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique or" production, combustion, is initiated in the carbonaceous stratum andv the resulting oombustion zone is caused to move thru, the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in the stratum is a direct air drive process for eiiecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difliculty and to permit the continued progress of the combustion zone thru the stratum, inverse air injection has been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means and air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In in situ combustion operations involving the passage of a combustion front from one or more ignition boreholes to one or more adjacent or surrounding boreholes, the heat losses in the top and bottom sections-of the carbonaceous stratum are greater than in the intermediate section thereof and require a larger minimum quantity of air flowing thru the upper and lower sections in order to maintain self-sustaining combustion. In operation of such a process, the flow of air is usually substantially the same at different levels in the stratum. This results in faster movement of the combustion front thru the intermediate section of the stratum than thru the adjacent sections and eventually the fire front becomes irregular and portions of the stratum may be bypassed by the combustion zone, thereby leaving unrecovered hydrocarbon in the stratum.

Accordingly, it is an object of the invention to provide an improved in situ combustion process for the recovery of hydrocarbons from a carbonaceous stratum. Another object is to provide an in situ combustion process for recovery of hydrocarbons which moves the combustion front more nearly uniformly thru the carbonaceous stratum than do conventional processes. A further object is to provide an in situ combustion process which efiects maximum recovery of hydrocarbons from a carbonaceous stratum. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.-

A broad aspect of the process of the invention cornprises establishing combustion of carbonaceous material in a stratum containing same across a transverse section of the stratum extending from the underburden to the atei'i'i' ice overburden adjacent the stratum and feeding o -containing gas to the resulting combustion zone at a faster rate adjacent the underburden and overburden than thru the intermediate section of the stratum. Feeding o -containing gas at a faster rate to the upper and lower sections of the stratum than to the intermediate section may be accomplished either by faster flow rate of a given gas to the upper and lower sections than to the intermediate section or by feeding a gas of higher 0 concentration to these sections than to the intermediate section. In other words, if air is the O -containing gas fed to all three sections, the air flow rate to the upper and lower sections must-be faster than to the intermediate section; however, a similar result may be obtained by feeding O -enriched air to the upper and lower sections while feeding air (unenriched) to the intermediate section. Obviously other concentrations of 0 than the normal concentration of about 20 percent in air may be utilized e.g., diluted air containing about 10 per cent 0 might be fed to the intermediate section of the stratum while air at normal 0 concentration is fed to the upper andlower sections of the stratum.

The process of the invention may also be effected by increasing the permeability of the upper and lower se tions of the stratum substantially above the permeability of the intermediate section so that when the cross section of stratum is subjected to a given pressure of air or other O -containing gas the flow rates thru the upper and lower (more permeable) sections are greater than thru the intermediate (less permeable) section so as to accomplish the objective of more rapid supply of O in the upper and. lower sections of the stratum.

Permeability may be increased by leaching with a. strong mineral acid in conventional manner as practiced in the petroleum production art or by selectively horizontally fracturing the stratum in conventional manner. Acid treatment of a selected layer of a stratum is eiiected by pack,- ing oil the selected layer around a borehole therein and forcing the acid into the stratum at the selected level so as to leach the same and increase the permeability thereof. In utilizing this technique, it is well to drive the acid by fluid pressure thru the selected level of the stratum to one or more boreholes therein spaced a few feet therefrom such as 5 to 50 or feet or more. A 5, 7, or 9- spot'well pattern may be utilized where a single ignition borehole is to be used. It is also feasible to utilize a series of in-line ignition boreholes and a parallel row of in-line injection boreholes on either side of the line of ignition borehole-s and parallel thereto.

After treatment of the stratum either by fracturingor acid leaching to increase the permeability thereof, the in situ combustion process is effected in conventional manner by igniting the carbonaceous stratum around one or more boreholes therein and driving the resulting combustion zone either by direct or inverse air injection thru the stratum to other boreholes therein.

vA more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation partly in section of an arrangement of apparatus in association with a carbonaceous stratum for effecting the process of the invention; and FIGURE 2 is a similar elevation of an air injection well or borehole showing an arrangement of apparatus for injecting streams of O -containing gas of different 0 concentration or for injecting O -c0ntaining gas of the same 0 concentration at diiferent rates 0 gas injection.

In FIGURE 1 a carbonaceous stratum 10, such as a tar sand, oil shale, or a porous type of coal such as lignite is penetrated by'an ignition borehole 12 and a series of in.- jection boreholes 14 surrounding the ignition borehole in a5, 7, or 9 spot well pattern. Two of the injection boreholes 14 are shown in this'figure. The embodiment illustrated in this figure involves fracturing the stratum at the levels adjacent the overburden and underburden so as to render the upper and lower levels of stratum 10 substantially more permeable than the intermediate section. It is of courses to be understood that a similar effect may be had by acid leaching of the upper and lower levels of the stratum between boreholes 14 and boreholes 12.

' Ignition borehole 12 is provided with tubing 16 on which is positioned a heater 18 for heating stratum 10 to ignition temperature. Tubing 16 extends to a level below "the bottom of stratum 10 so that liquid hydrocarbon produced in the process may be withdrawn substantially as fast as produced, thereby avoiding building up the level of liquid hydrocarbon into the stratum being produced. Heater 18 may be any downhole type of heater such as a gas-fired-heater, an electric heater, a mass of incandes cent charcoal, etc.

The various wells or boreholes shown in FIGURE 1 are provided with an air injection system comprising a pump or compressor 20, an air supply line 22, and individual well feed lines 24 and 26. An auxiliary air line 28 connects with tubing 16 for use when tubing 16 is free of produced fluids and it is desired to inject air thu the tubing.

- In FIGURE 2, injection well or borehole 14- is provided with a pair of concentric conduits 30 and 32, the latter extending to a lower level of the stratum and conduit 30 extending to an intermediate level thereof. A pair of packers 34 and 36 pack oif the intermediate section of the formation to establish communication between this section and the end of conduit 30, while the lower section communicates with the end of conduit 32. The upper levelor section of stratum 10 is open to the annulus 38 between conduit 30 and casing 40. Air injection line 42 communicates with the annulus between conduits 30 and 32 and feeds air to the intermediate section, while air lines 44 and 46 communicate with the lower and upper levels or sections of stratum 10 thru conduit 32 and annulus 38, respectively. Air line 48 is connectedwith injection lines 44 and 46 thru manifold 50.

Y The arrangement shown in FIGURE 2 permits injection of air at different rates into the upper and lower 3 sections of stratum than the air injection rate into the intermediate section of the stratum. It also permits the injection ofoxidizing gas of different 0 concentration to the upper and lower sections than to the intermediate section. In other words, lines 42 and 48 may be supplied with air at dilferent pressures and/or with combustionsupporting gases of different 0 concentrations.

Operating in accordance with one embodiment of the invention, stratum 10 is selectively fractured horizontally between ignition borehole 12 and boreholes 14 at the upper and lower levels of the stratum adjacent the overburden and underburden in known manner so as to in- .crease the permeability of the stratum at these levels. The

stratum is then ignited around borehole 12 by means of a suitable heater 18 in known manner, such as by heating the stratum to ignition temperature and injecting air into the same to establish a combustion zone around the borehole. After the combustion zone is established, it is driven thru the stratum to surrounding boreholes 14 either by direct drive with air injected thru borehole 12 or by in the layers of stratum 10 adjacent the overburden and adjacent the underburden than thru the intermediate section of the stratum so as to effect more uniform movement of the combustion zone thru the stratum at the different levels therein. A similar result may be obtained where the permeability of the upper and lower layersis increased by acid leaching. l -In applications of the-process involving increasing the air pressure on the upper and lower levels of the stratum as compared to the intermediate section thereof, or in that embodiment of the invention in which the concentration of oxygen is greaterin the gas supplied to the upper and lower levels of the stratum than to the intermediate section, boreholes 14 are equipped as shown in FIGURE 2. With this arrangement of apparatus in the injection boreholes the combustion front is moved thru the stratum from ignition borehole 12 either by faster air flow rates thru the upper and lower levels of the stratum than thru the intermediate section or by means of combustion-supporting. gas of higher oxygen concentration thru the upper and lower levels thereof.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

We claim:

1. In a process for producing hydrocarbons from a section of a permeable carbonaceous stratum located between an overburden and an underburden, between an ignition borehole and an ofiset borehole therein by in situ combustion which comprises igniting said stratum along the wall of said ignition borehole from the overburden to the underburden of the stratum; feeding O -containing gas to the resulting combustion zone thru one of said boreholes so as to move said combustion zone thru said section of stratum toward the other borehole; and recovering produced hydrocarbons thru one of said boreholes, whereby the progress of said zone thru said stratum is slower adjacent said overburden and underburden than in the intermediate section of stratum due to heat loss to said overburden and underburden; the improvement comprising packing off an upper section of said stratum adjacent said overburden and a lower section adjacent said underburden and providing separate gas flow passageways to each said section and to said intermediate section; feeding the O in said gas to said combustion zone thru said intermediate section at a given rate and feeding the O in said gas thru said upper and lower sections adjacent the overburden and underburden at a higher rate so as to burn said sections faster than would occur with said given rate, compensate for said heat loss, and effect more uniform progress of said combustion zone between said boreholm.

2. The process of claim 1 wherein O is fed at a faster rate to the sections adjacent said overburden and underburden'by feeding a gas richer in 0 thereto than thru said intermediate section.

3. The process of claim 1 wherein said gas is fed at a faster rate to the sections adjacent said overburden and underburden than to said intermediate section.

4. The process of claim 3 wherein said gas is air.

5. The process of claim l' wherein ignition is estab lished around a centrol borehole and said combustion zone is advanced toward a ring of surrounding boreholes in said stratum.

. 6. The process of claim 5 wherein said gas is injected thru said central borehole to advance said combustion zone and production is recovered thru said ring of boreholes.

7. The process of claim 5 wherein said gas is injected thru said ring of boreholes to move said combustion zone countercur-rently to flow of said gas and production is recovered thru said central borehole.

8. A process for producing hydrocarbons from a permeable carbonaceous stratum located between an overburden and an underburden, which comprises increasing the permeability of said stratum from one borehole to another borehole therein thru'sections adjacent the overburden and the, underburden by packing oflf said sections within at least one of the boreholes and injecting a strong mineral acid into the packed off sections t-hru one of said boreholes to increase the void space in the stratum in said sections while leaving the permeability of the intervening section of stratum substantially unchanged, thereby decreasing the resistance to flow of gas between said boreholes thru said sections; igniting said stratum along one of said boreholes to establish a combustion zone extending from said overburden to said underburden; advancing said combustion zone thru said stratum toward the other borehole by pressurizing one of said boreholes with an o -containing, combustion-supporting gas whereby said gas is fed at a faster rate thru said sections than thru said intervening section to compensate for greater heat losses in said sections than occurs in said intervening section; and recovering produced hydrocarbons from one of said boreholes.

9. The process of claim 8 wherein said stratum is ignited around a central borehole; said gas is injected into said stratum thru a series of surrounding boreholes so as to feed said combustion zone; and said central borehole is utilized as a production borehole.

10. The process of claim 8 wherein ignition is effected in a series of in-line ignition boreholes, and air is injected into said stratum thru a series of in-line injection boreholes substantially parallel with the line of ignition boreholes and combustion in said stratum is advanced toward said injection boreholes by injecting air therethru, with production being recovered thru said ignition boreholes.

11. A process for producing hydrocarbons from a permeable carbonaceous stratum located between an overburden and an underburden, and penetrated by a pair of boreholes, which comprises packing off an upper section of said stratum in at least one of said boreholes; fracturing the packed ofi sections by applying fluid pressure thru the packed oif sections so as to increase the effective permeability thereof while retaining the original permeability of the intervening section of stratum; ignit- References Cited in the file of this patent UNITED STATES PATENTS 2,143,251 Savitz Jan. 10, 1939 2,754,911 Spearow July 17, 1956 2,793,696 Morse May 28, 1957 2,813,583 Marx Nov. 19, 1957 2,818,118 Dixon Dec. 31, 1957 2,819,761 Popham Jan. 14, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,004,596 October 17 1961 Harry W. Parker et al. I

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read as "corrected below.

Columr} 6 lines 2 and 3 after "section" insert and a lower section Signed and sealed this 8th day of May 1962.

SEAL) Attest:

ERNEST w. .SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents 

11. A PROCESS FOR PRODUCING HYDROCARBONS FROM A PERMEABLE CARBONACEOUS STRATUM LOCATED BETWEEN AN OVERBURDEN AND AN UNDERBURDEN, AND PENETRATED BY A PAIR OF BOREHOLES, WHICH COMPRISES PACKING OFF AN UPPER SECTION OF SAID STRATUM IN AT LEAST ONE OF SAID BOREHOLES, FRACTURING THE PACKED OFF SECTIONS BY APPLYING FLUID PRESSURE THRU THE PACKED OFF SECTIONS BY APPLYING FLUID PRESEFFECTIVE PERMEABILITY THEREOF WHILE RETAINING THE ORIGINAL PERMEABILITY OF THE INTERVENING SECTION OF STRATUM, IGNITING SAID STRATUM ALONG ONE OF SAID BOREHOLES TO ESTABLISH A COMBUSTION ZONE EXTENDING FROM SAID OVERBURDEN TO SAID UNDERBURDEN, ADVANCING SAID COMBUSTION ZONE THRU SAID STRATUM TOWARD THE OTHER BOREHOLE BY PRESSURIZING ONE OF SAID BOREHOLES WITH AN O2-CONTAINING, COMBUSTION SUPPORTING GAS WHEREBY SAID GAS IS FED AT A FASTER RATE THRU SAID UPPER AND LOWER SECTIONS THAN THRU SAID INTERVENING SECTION TO COMPENSATE FOR GREATER HEAT LOSSES IN SAID SECTIONS THAN OCCUR IN SAID INTERVENING SECTION, AND RECOVERING PRODUCED HYDROCARBONS FROM ONE OF SAID BOREHOLES. 